3 Answers
3

//dupe_node[1] is generally wrong, although it produces an identical result in this particular case. See docs:

The location path //para[1] does not mean the same as the location path /descendant::para[1]. The latter selects the first descendant para element; the former selects all descendant para elements that are the first para children of their parents.

Given the following XML:

<foo>
<bar/>
<foo>
<bar/>
</foo>
</foo>

//bar[1] will produce two nodes, because both bars are first children of their respective parents.

/descendant::bar[1] will give only one node, which is the first of all the bars in the document.